Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for(keyinfoo){doSomething(key);}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see no-prototype-builtins.

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.